1. Field
Embodiments described herein relate generally to a magnetic resonance imaging apparatus.
2. Description of the Related Art
A magnetic resonance imaging apparatus is an apparatus that images an inside of a subject by using a magnetic resonance phenomenon. Such magnetic resonance imaging apparatus includes various units, such as a static magnetic-field magnet that generates a static magnetic field in a scan region, a gradient coil that applies a gradient magnetic field onto the subject placed in the static magnetic field, and a radio frequency coil that receives a magnetic resonance signal from the subject applied with the gradient magnetic field.
Among the various units, the gradient coil is repeatedly supplied with a pulse current while imaging, thereby generating heat to a large extent. Especially in recent years, a speedup in switching of a gradient magnetic field and an enhancement of the strength of a gradient magnetic field are strongly required along with a speedup in an imaging technology, so that heat generation by a gradient coil becomes more marked.
Heat generation by a gradient magnetic field has a possibility of giving influence on the quality of a taken image, or giving a pain to a subject to be imaged. For this reason, conventionally, various technologies for suppressing heat generation by a gradient coil while imaging have been invented. For example, a technology of cooling a gradient coil while imaging by circulating a coolant through cooling pipes provided inside the gradient coil has been proposed (for example, see JP-A 2006-311957 (KOKAI)).
However, according to conventional magnetic resonance imaging apparatuses, there is a problem that the gradient magnetic field cannot be uniformly cooled, as described below.
Specifically, according to the conventional technology described above, an inlet and an outlet of a cooling pipe is generally arranged on opposite sides in the gradient coil. During a period from flowing in from one side of the gradient coil until flowing out from the opposite side, a coolant flowing through the cooling pipe gradually rises in temperature by taking up heat generated by the gradient coil. Therefore, a difference is made in the temperature of the coolant between the vicinity of the inlet and the vicinity the outlet of the cooling pipe. As a result, a temperature gradient occurs in the cooling water flowing through inside the gradient magnetic field, so that the gradient coil cannot be uniformly cooled.